Method of briquetting finely divided ores



2,755,177 Patented July 17, 1956 2,755,177 METHOD OF BRIQUlgIgIgIG FINELY DIVIDED John H. Crowe, Lakeland, Fla assignor to Minerals & Chemicals Corporation of America, a corporation of Maryland No Drawing. Application November 1, 1952, Serial No. 318,348

9 Claims. (Cl. 753) This invention relates to the briquetting of finelydivided ores, particularly those containing iron oxide, so as to render them suitable for charging into a blast furnace. Such solids, for reasons well known, cannot be charged directly into the furnace and must be formed into briquettes or other suitable agglomerates.

Large quantities of finely-divided iron oxide ores are produced in the so-called washing of iron ores. Usually these products must be submitted to a concentration operation in order to raise their iron oxide content sufiiciently to make them suitable for smelting. It is to the treatment of such concentrates to form briquettes or other suitable agglomerates that this invention is particularly directed, although the process is not limited to such material and may be applied to any form of finely-divided iron oxide material, such as, for instance, flue dust pro duced in blast furnaces.

Such briquettes or other agglomerates must be sufficiently durable to withstand, with negligible dusting, all

stresses on them during storage, handling, furnace residence (before reduction) etc.; they should also be waterresistant enough to survive open storage in all weathers, with negligible alteration in size or quality.

The present invention comprises a method of making strong and water-resistant iron ore briquettes or agglomerates. I have found that a small quantity of a mixture of waste sulfite liquor and any one of the chromium compounds hereinafter described, when mixed with iron ore concentrates prior to briquetting or otherwise agglomerating said concentrates, acts as a binder and water-proofing agent in the finished briquettes or agglomerates. Very little pressure is required for forming briquettes or agglomerates containing the mixtures of sulfite liquor and chromium compounds. These mixtures set to insoluble jellies and it is thought that these jellies impart the necessary strength and water-resistance properties to the briquettes.

Experiments indicate that the lignin content of the sulfite liquor is the active ingredient which causes the formation of the jelly although I do not wish to be limited by any theories as to the action of these ingredients. This method of agglomeration is superior to other known methods, in that it entails no thermal hardening treatment at high temperatures with its attendant costly high heat requirement and, in some cases, surface glazing of the briquettes which impairs their porosity.

ore fines, sulfite liquor and a chromium compound (which may be a dichromate, a water-soluble chromate or chromic acid) is obtained by masticating the mixed ingredients in some manner, for example, in a pug mill, and then molding this mixture into briquettes under pressure only just sufiicient to form them. These briquettes are then heated to and held at about 250 F. long enough to drive off the non-essential moisture, after which they possess adequate mechanical strength and weather resistance for stock-piling, shipping and blast furnace rigors. Obviously, instead of being made into briquettes the material may be agglomerated by extrusion or other methods.

Example A sample of damp hematite concentrates, containing about 10% (total weight basis) moisture, was placed in a mechanical laboratory mixing device. A solution of sodium dichromate in waste sulfite liquor from a paper mill using western hemlock was made up and added to the iron ore in the mixer. The quantities of the ingredients of the mixture involved in this example were: Hematite concentrates, 1000 grams (dry basis); sulfite liquor, 60 grams; and sodium dichromate, 3 grams.

The mixer was operated for one hour and then briquettes were formed from the ore mass by means of a hand press. The briquetting was accomplished by a steady increase in compression till the briquettes were firm and well-packed, at which time the pressure was suddenly released.

The resulting briquettes, after standing overnight in the room air, were placed in an oven in which the temperature was maintained at about 250 F., and were kept there for one hour. After they had cooled to room temperature, they were tested for weather resistance by immersion in water. After two hours under water the briquettes contained cracks around the edges but were otherwise unchanged in appearance. Briquettes made of hematite concentrates in the same way as above described but without additives, start disintegrating immediately upon being placed in water, and within a few minutes are mostly slime.

Iron ore briquettes containing sulfite liquor and sodium dichromate and made in the manner described proved capable of withstanding temperatures up through 1500 F. without changing in size or physical appearance except for color. Moreover, briquettes made in the manner above described with sulfite liquor and sodium dichromate were much tougher than those made with no additives, as was proven by the results of tumbling and other tests.

00 In putting this invention into practice, a blend of iron l have found that jellies useful in this method are formed when water-soluble chromates are dissolved in sulfite liquor, when chromic acid is dissolved in sulfite liquor, and when dichromates are dissolved in sulfite liquor; but on account of their lower cost I prefer to use an alkali dichromate as the gelling agent. I have found that about 3% of the dichromate calculated on the weight of sulfite liquor is normally suflicient to cause formation of the required jelly although I prefer to use 10% which causes the jelly to set more quickly.

Sulfite liquors from two widely separated paper mills, one in Florida (using pine wood) and the other in the state of Washington (using western hemlock) were each gelled by the addition of sodium dichromate. Since I have found that lignin from pine wood, when made into an aqueous solution having about the specific gravity of sulfite liquor and treated with sodium dichromate, forms a jelly similar to the sulfite liquor-dichromate jelly, I believe that ligin is the ingredient of the sulfite liquor which is responsible for the formation of the jelly.

What I claim is:

1. The method of aggl f crating finely divided iron oxide material which comprises mixing the said material with an aqueous solution of ligin containing at least one chromium compound selected from the group of dichromates, water-soluble chromates and chromium trioxide to form a plastic mass, forming said mass into ag glomerates, and removing any excess moisture from said agglomerates.

2. The method of agglomerating finely divided iron oxide material which comprises mixing the said material with an aqueous solution of sulfite liquor containing at least one chromium compound selected from the group of dichromates, water-soluble chromates and chromium trioxide to form a plastic mass, forming said mass into agglomerates, and removing any excess moisture from said agglomerates.

3. The method of preparing agglomerates from iron ore concentrates which comprises mixing said concentrates with a solution of an alkali dichromate in sulfite liquor to form a homogeneous plastic mass, molding said mass into agglomerates, and drying the agglomerates at temperatures of between about 220 F. and 300 F.

4. The method of forming briquettes from finely divided iron oxide material which comprises mixing said material with solutions of lignin and a chromium compound selected from the class of dichromates, soluble chromates and chromium trioxide to form a plastic mass, and forming said mass into briquettes and drying same.

5. The method of forming briquettes from finely divided iron oxide material which comprises mixing said material with sulfite liquor and a chromium compound selected from the class of dichromates, soluble chromates and chromium trioxide to form a plastic mass, and forming said mass into briquettes.

6. The method of briquetting finely divided iron ore concentrates which comprises mixing with said concentrates sulfite liquor to which has been added an alkali dichromate in the amount of not more than 1% based on the weight of the iron ore concentrates, to form s plastic mass, forming briquettes from said mass, and removing excessive moisture therefrom.

7. An agglomerate composed of finely divided iron ore concentrates united by a mixture of an aqueous solution of lignin and a chromium compound selected from the group of dichromates, water-soluble chromates and chromium trioxides from which agglomerate excessive moisture has been removed.

8. A briquette composed of finely divided iron ore concentrates united by a mixture of an aqueous solution of lignin and an alkali dichromate from which briquette excessive moisture has been removed.

9. A briquette composed of finely divided iron ore concentrates united by a mixture of sulfite liquor and an alkali dichromate from which briquette excessive moisture has been removed.

References Cited in the file of this patent UNITED STATES PATENTS 1,013,614 Robeson Ian, 2, 1912 1,158,366 Bibb Oct. 26, 1915 2,052,329 Wendeborn Aug. 25, 1936 2,460,811 Davies et a1. Feb. 8, 1949 

1. THE METHOD OF AGGLOMERATING FINELY DIVIDED IRON OXIDE MATERIAL WHICH COMPRISES MIXING THE SAID MATERIAL WITH AN AQUEOUS SOLUTION OF LIGIN CONTAINING AT LEAST ONE CHROMIUM COMPOUND SELECTED FROM THE GROUP OF DICHROMATES, WATER-SOLUBLE CHROMATES AND CHROMIUM TRIOXIDE TO FORM A PLASTIC MASS, FORMING SAID MASS INTO AGGLOMERATES, AND REMOVING ANY EXCESS MOISTURE FROM SAID AGGLOMERATES. 